Indicator means for indicating the



Feb. 14, 1956 E. G. BENEDICT INDICATOR MEANS FOR INDICATING THE CONDITION OF FUSES Fig.2

Filed Jan. 9, 1952 Fig.1

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United States Patent INDICATOR MEANS FOR INDICATING THE CONDITION OF FUSES Earl G. Benedict, Cobleskill, N. Y.

Application January 9, 1952, Serial No. 265,654

2 Claims. (Cl. 200-121) This invention relates to means for indicating the condition of fuses and of other electrical circuits elements and it has for its primary purpose to provide an inexpensive, simple and reliable indicator for producing an unmistakable indication for the blowing of a fuse or for the breaking of an electric circuit at a certain point which method does not entail the use of attachments or of auxiliary apparatus while it permits unskilled persons to spot a blown fuse or broken circuit at a glance among a large number of indicators.

Numerous ways of indicating the condition of fuses and of other protective circuit controlling elements have been proposed. The most common method of indicating the condition of a fuse consists in providing the fuse container with a transparent closure wall, wall portion or cap, the transparent member or portion permitting inspection of the fuse wire. However, it is extremely difficult for the average person not skilled in electric work to distinguish a blown fuse from an intact fuse, especially when fuses, as usual, are arranged in large numbers.

Fuse rupture indicating methods which involve the use of mechanical structures are excluded, as regulations prohibit the introduction of mechanical means or gadgets into the fuse container. Detecting methods must thus be associated with the fuse or with the container, or with the electrodes, or with the filling substance, if any.

Indication by thermic action or by a chemical reaction has also been proposed. The thermic action is usually produced in a special attachment to the fuse carrying a member heated by the current when the fuse is blown. The heat thus produced drives out moisture or in .some other way changes the color of a substance surrounding the heated wire. This thermic method is however only usable with an attachment for each fuse arranged in parallel and is also rather complex. The chemical methods use either a coating of the fuse wire with a substance reacting when heated or a special disk or plate which must be introduced into the fuse container and which is coated with substances which are ignited by the blowing of the fuse or which start to react at the temperature produced by the melting of the fuse link. The first named method furnishes a. poor indication and the last named method is objectionable insofar as a rather large object namely the coated disk must be introduced into the fuse container and must be in contact with the fuse link.

The methods for indicating the blowing of the fuse by thermic action or chemical reaction moreover are usually subject to the disadvantage that changes of moisture in the atmosphere and temperature changes occurring in the surroundings may produce the change which should be initiated only by the blowing of the fuse.

According to the invention an indicator is used which is not based on the production of heat upon melting of the fuse but which is based on the fact that the melting of a fuse invariably produces a discharge between the ruptured ends which in its turn produces ozone within the small air voltune of the container. Ozone is easily 2,734,967 Patented Feb. 14, 1956 detectable as it is chemically very active. Ozone detecting substances therefore may be deposited in form of a layer at any place on the inside of the fuse container in such a way that they are visible from without through a transparent wall or cap and as the detector consists merely in a coating its presence within the fuse container is not objectionable. The substances serving as an indicator need not be in contact with the fuse wire and need not be positioned in its immediate vicinity.

Moreover, such ozone detectors are not alfected by weather, temperature or moisture conditions existing on the spot on which they are mounted or to which they have been subjected before mounting them.

That ozone is always produced when a fuse blows follows from the condition which invariably produces the fuse blow out. Practically the fuse blows either upon the occurrence of a current surge which may be due to a short circuit or the like during which current surge high amperage values are reached, or the fuse blows with relatively low amperage values on account of an overload which slowly heats the fuse wire until it reaches its melting temperature. In the first named case the fuse link is severed into a plurality of segments accompanied by an electric discharge between the segments at the moment of severing. In the second case the fuse link softens and is ruptured usually at one point only when the melting temperature has been reached or is very closely approximated. An electrical discharge between the ruptured parts is again produced in the moment of the rupture.

The presence of ozone may be detected by its oxidizing action on mercury or silver.

A preferred method of detecting ozone is however by means of dyestuffs which either are colored or are discolored by oxidation due to ozone or by virtue of the addition of an ozone link across a double link between carbon atoms. The first type of dyes are usually colorless in an unoxidized state and are known as leuco dyes or leuco-bases; they are colored when oxidized by ozone.

The method of addition which has been above mentioned uses colored dyes which upon reaction with ozone form products known as ozonides, the ozone being added across a C=C group. The reaction may be described by the following general formula.

In all dyes in which C=C is the chromophore group, that is a group responsible for the colored appearance the formation of ozonides leads to decoloration so that the presence of ozone and the occurrence of a spark or arc is immediately detected.

An example for a dye of the above type is indigo. Its reaction with ozone is described by the formula:

Indigo Ozonide (colorless) An example for a leuco dye which is colorless in an unoxidized state and is colored by its reaction with ozone 3 is indigo white (biindozyl, leuco-indigo) C1eH12OzN2 having the formula from which in the presence of ozone indigo C1sH1oO2N2 is formed.

As above stated indigo is only a representative of a group of dyes such as for example the triphenyl-methone dyes, diphenyl methan dyes the stilbene dyes, the phthalein and acridin dyes and several others which have a chromophore C=C group and from which therefore in the presence of ozone ozonides are formed.

The main point in the selection of this group of dyes is that they permit to distinguish between the reaction with ozone molecules and the reaction with the normal oxygen molecule of the air. As both are forms of the same element and as the reaction with ozone is essentially merely an oxidation, the substances to be selected which form an indicator must be of such a character that oxidation in air does not take place or requires a very long time to take place while the reaction with ozone which is a chemically more active form, takes place instantaneously. The dyes of the above group show such a reaction, indigo being the best example.

The use of leuco dyes, while having the advantage of giving a more conspicuous indication, have the disadvantage that their oxidation period with oxygen of the air is shorter than the oxidation period of the corresponding dye with a chromophore group. Their use is therefore more limited or entails the use of sealed fuse containers filled with an inert gas.

The indicator which may be used in connection with the method above described is shown by way of example in the accompanying drawing, but it is to be understood that the container which has been illustrated is in itself a known construction and shown by way of example only and any one of the known constructions may be substituted without in any way departing from the invention.

In the drawing:

Figure l is an elevational sectional view of a fuse plug.

Figure 2 is an elevational view of a fuse cartridge.

The construction of the fuse plug shown in Figure 1 is conventional. The substantially cylindrical insulating body 5 is surrounded by the threaded metallic sleeve 6 forming one of the contacts of the plug while at. the base a central contact 7 is arranged. The plug has a central cavity 8 containing the fuse wire 10 which is connected with the two contacts. In order to establish a connection the central contact 7 is provided with a pin reaching into the cavity to the end of which the fuse wire 10 has been soldered. The other end of the fuse wire passes through a small hole in the body and is soldered to the sleeve 6. The cavity 8 is closed by a transparent heat resisting material for instance, by a sheet of mica 9, of glass or the like.

The transparent sheet 9 may carry a coating 11 of the ozone detecting material and the color of the coating 4 indicates to the observer whether a spark or are has occurred within the closed cavity 8 and therefore whether the fuse wire is in tact or has been blown. Any discharge occurring within the cavity 8 and developing ozone will cause a change of color of the coating.

The coating need not be applied to the transparent cover sheet but may also be applied to the bottom of the cavity to be viewed through the transparent sheet as indicated at 12 by the dotted line.

in Figure 2 the cartridge type fuse container 14 is shown having sleeves 15 to be inserted between clamps (not shown) serving as contact electrodes. The central portion 16 is transparent. The fuse is shown as formed by a ribbon 18 of a suitable metal which is slightly notched in order to produce a breaking of the fuse at apredetermined point.

Indicating dye may either be applied to the back portion of the cartridge viewed through the transparent portion 16 or may be applied to both sides of the ribbon 18 facing the transparent portion.

It will be understood that the above described method may also be used in conjunction with other circuit elements, enclosed in a container, for indicating the breaking of a circuit and a consequent are or spark formation. For instance, the method may be used in connection with safety switches which do not have a fusible element but have contact arms or contact springs which separate upon occurrence of an overload or of a current surge, thus producing an are or spark which leads to ozone formations.

It will further be understood that unessential deviations from the method above explained will not constitute a departure from the principle of the invention as defined in the annexed claims.

Having described the invention, what is claimed as new is:

1. An electric fuse device having a fusible element, comprising a housing surrounding said fusible element, a coating of an ozone detecting dye having a chromophore group from which ozonides are formed on one of the walls of the housing, said coating changing its color upon appearance of ozone in the air contained in the housing, said ozone being produced by an-electric discharge following melting or rupture of the fuse wire.

2. An electric fuse device having a fusible wire element, comprising a housing surrounding said fusible wire element, a coating of indigo white changing its color upon appearance of ozone in the air contained in the housing, said ozone being produced by an electric discharge following rupture of the fusible wire element.

References Cited in the file of this patent UNITED STATES PATENTS 636,379 Erikson Nov. 7, 1899 856,292 Phelps June 11, 1907 1,666,339 Miller Apr. 17, 1928 1,857,019 Hassell et al. May 3, 1932 2,442,216 Skeats May 25, 1948 OTHER REFERENCES Vosmaer: Ozone published by D. Van Nostrand Co., N. Y., 1916, 197 pages, pages 19, 22 and 41. 

